There are circumstances where disposing of a slurry comprised of water and debris requires a separation of the liquid and solid phases. Such a circumstance occurs when vehicles used in dirty operations, such as construction or fire-fighting, and particularly in operations where there is an exposure to contaminants, are washed in a post-service cleanup. Commonly, the collected debris is comprised of mud, but may also comprise a suspended element which is harmful to life or to the environment. Accordingly, the solids in the slurry must be separated for safe disposal. Even if hazard is not an issue, it would be desirable for cost purposes to avoid transporting the water weight to a disposal site.
The cleaning process may occur over a mat or a containment system that collects the runoff water and debris. The slurry is then pumped from the mat to a settling tank to allow separation by gravity. The sludge that precipitates is then shoveled into sand bags, which are loaded onto pallets and evacuated by fork lift and truck transport to a land fill. The process, wherein bags of up to fifty pounds are loaded and lifted by hand, is labor intensive and prone to back injuries.
When the washing is done in a backwoods location, for example, both access and expense are involved in bringing a rough terrain fork lift to the location.
A portable settling tank offers an advantage in such a case because transferring the sludge in sand bags can be avoided. The portable tank would be moved directly to the land fill site after a dewatering process on location. U.S. Pat. No. 4,929,353 to Harris and U.S. Pat. No. 5,595,654 to Caughman both disclose portable dewatering tanks. In both Harris and Caughman, a filter medium is supported by a structure internal to the tank which is designed to create a cavity for drainage around the structure. Dewatering involves draining the filtrate from the cavity. When transported to the disposal site, the sludge must be removed from the structure and cleaned along with the tank. In the case of Caughman, the filter medium must also be cleaned.
The present invention is directed to an improvement in the art of portable settling tanks, wherein a thin slurry may be efficiently separated into liquid and solid components, and the resulting residue removed by dumping the contents of the tank in a manner where no cleaning is required.